The present invention relates generally to the fields of organic and analytical chemistry and more particularly to a denivatizing agent and method for detecting and quantifying isocyanate contamination in a sample, such as an environmental sample.
Isocyanates are a class of organic compounds, containing the isocyanate functional group xe2x80x94Nxe2x95x90Cxe2x95x90O. Isocyanates are used in the production of a wide variety of products, such as herbicides, crop protecting agents, antidiabetic agents, and polyurethane materials, including foams for insulation, seating, and paints with durable finishes. The most common isocyanates employed in industry are 2,4- and 2,6-toluene diisocyanate (TDI), 4,4xe2x80x2-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), and isophorone diisocyanate (IPDI).
Although isocyanates are commercially beneficial, they have been known to create significant health risks. For example, isocyanates are severe respiratory irritants and can cause irritation of the eyes and mucous membranes. Prolonged exposure may result in permanent respiratory impairment. Because of the serious health risks associated with the use of isocyanates by industrial workers, most industrialized countries have set limits on the permissible levels of exposure. For example, the National Institute for Occupational Safety and Health (NIOSH) in the United States has set a level of 5 ppb; the Deutsche Forschungsgemeinschaft in the Federal Republic of Germany has set a limit of 10 ppb; and the Health and Safety Executive of the United Kingdom has created a standard of 20 xcexcg NCO mxe2x88x923 for an eight hour time-weighted average and 70 xcexcg NCO mxe2x88x923 for a ten minute time-weighted average.
In many environments, the hazard posed by isocyanate contamination in the air is not limited to a single isocyanate species. Products made using isocyanates may contain several different isocyanate species and new species may be released during use of the product. Therefore, it is important to assess the total hazard resulting from exposure to isocyanates, which requires measuring all isocyanate species. However, analytical standards are unavailable for a majority of these species, preventing individual identification of all isocyanate species in routine sample analysis.
A number of methods for measuring isocyanate monomers have been developed. Many of these are reviewed by Pumnell, el al. (Analyst, 110:893-905, 1985) and Dharmarajan, et al. (Sampling and Calibration for Atmospheric Measurements: 190-202, 1987). Almost all of these analytical methods are based upon the measurement of certain individual isocyanate species and, therefore, cannot measure total isocyanate concentration.
Marcali (Anal. Chem., 29(4): 552-58, 1957) describes a calorimetric method for the measurement of isocyanate monomer. The Marcali method is limited to the measurement of aromatic isocyanates. Furthermore, the Marcali method is susceptible to interferences, exhibits poor sensitivity when compared with standard chromatographic methods, and the response varies with isocyanate structure.
Another method currently used to measure isocyanates is Method 25 for the Determination of Hazardous Substances (MDHS 25) of the Health Safety Executive of the United Kingdom. This method employs 1-(2-methoxyphenyl)-piperazine (MOPP) to derivatize isocyanate species. The derivatives are then analyzed with high performance liquid chromatography (HPLC) using ultraviolet and electrochemical detectors in series (HPLCJUV/EC). (Health and Safety Executive: Occupational Medicine aid Hygiene Laboratory, March 1987). Bagon, et al. (Am. Ind. Hyg. Assoc. J., 45(1):39-43, 1984) disclose the use of MDHS 25 for determining isocyanate monomers and prepolymer relative to a monomer standard. The MDHS 25 method has been found to be unreliable in its ability to correctly identify isocyanate species and inaccurate in its quantitation of those species. (Streicher, et al., Am. Ind. Hyg. Assoc. J., 56: 437-42, 1995).
A similar method has been developed by Wu, et al. (Analyst, 116(1): 21-5, 1991), in which tryptamine is employed as a derivatizing reagent followed by detection of the derivative using HPLC with fluorescence and electrochemical detectors in series. Although the Wu, et al. method appears to give more selective detection with less response factor variability than the IMDHS 25 method, all compounds must elute as observable peaks, and the analysis assumes that all isocyanates derived from a particular monomer have the same detector response factor. However, it has been found that the detector response factors of several tryptamine-derivatized isocyanates vary significantly. This method also requires the use of two detectors to confirm the identity of peaks as derivatized isocyanates.
U.S. Pat. No. 3,533,750 to Belisle discloses a process for detecting toluene diisocyanate, other aromatic isocyanates, or aromatic amines in ambient air. The method involves contacting an air sample with an acid solution of glutaconic aldehyde and then with a cationic ion exchange resin. The isocyanate is converted to a corresponding amine that is reacted with a reagent to produce a yellow color that is concentrated on the surface of the resin. Although the method is quick and sensitive, it cannot be used to detect aliphatic isocyanate species.
Schmidtke, et al. (Fresenius J. Anal. Chem., 336(8): 647-54, 1990) teach a sensitive high performance liquid chromatographic procedure to analyze hexamethylene diisocyanate (HDI), 2,4- and 2,6-toluene diisocyanate (TDI) and 4,4xe2x80x2-diphenylmethane diisocyanate (MDI) in air. The isocyanates are trapped on a sorbent coated with 1-(2-methoxyphenyl)piperazine (MOPP). The resulting derivatives are separated using a column switching technique employing either a diode array UV detector or an electrochemical detector.
Hanus, et al. (Mikrochimica Acta, 3(1/6): 197-206, 1988) disclose the use of tubes packed with Chromosorb WAW, end-plugged with glass wool and impregnated throughout with 1-(2-pyridyl)piperazine for collection and in situ derivatization of toluene 2,4-diisocyanate (TDI), 4,4xe2x80x2-diphenylmethane diisocyanate (MDI) and 1,6-hexamethylene diisocyanate (HDI), which are collected from air. The compounds are desorbed and detected by ion-pair chromatography using a LiChrosorb RP-18 column.
Dalene, et al. (J. Chromat., 435: 469-81, 1988) disclose a high performance liquid chromatographic method for the trace analysis of complex air mixtures containing 2,6- and 2,4-toluene diisocyanates and related amino isocyanates and diamines. The method is based on derivatization of the isocyanate functional groups to corresponding urethane groups with alkaline ethanol as the sampling and reacting medium.
Wu, et al. (Am. Ind. Hyg. Assoc. J., 47(8): 482-87, 1986) describe a procedure for detecting isophorone diisocyanate (1-isocyanato-3-isocyanatomethyl-3,5,5-trimethylcyclohexane) by drawing air through a solution containing one of the following derivatizing agents: 1-(2-methoxyphenyl) piperazine, N-(4-nitrobenzyl)propylarine, or dibenzylamine. The reaction forms the corresponding urea derivatives which are then determined by HPLC using a LiChrosorb RP-18 column. Although relative recoveries are good (97-104%), the stability of the isophorone diisocyanate solution is low, having a half-life of approximately 3.8 days in acetonitrile.
The determination of isocyanates in air by nornal-phase liquid chromatography with fluorescence detection is described by Kormos, et al. (Anal. Cheni., 53(7): 1122-25, 1981). The isocyanates are converted to the N-methyl-1-naphthalenemethylamine (MNMA) urea derivatives.
The foregoing methods are incapable of correctly identifying or accurately quantifying all isocyanate species that may be present in a sample. Thus, there is a need for a simple method for detecting total isocyanate in an environmental sample, such as a solid, liquid, or air sample or a surface wipe sample.
A novel isocyanate derivitizing agent, useful for the determination of isocyanates in a sample, such as an environmental sample, is provided. The agent is 9-anthracenylmethyl-1-piperazinecarboxylate, referred to herein as xe2x80x9cPAC.xe2x80x9d A method for producing PAC and a method for measuring the total level of isocyanate in an environmental sample are also provided.
PAC has the following chemical structure: 
PAC is produced by adding 9-anthacenemethanol and pyridine to a solution of p-nitrophenyl chloroformate. Product is isolated to provide a crude anthrylmethyl p-nitrophenyl carbonate, which is then added to a solution of piperazine. The reacted mixture is poured into water and extracted with a solvent, preferably an organic solvent such as toluene. The product is washed and dried to provide 9-anthracenylmethyl-1-piperazinecarboxylate (PAC).
In accordance with the isocyanate detection method, a derivatizing agent such as PAC or a similar compound is used in conjunction with any conventional type of environmental sampling device, such as an air sampling device, to detect the total amount of isocyanate present in the sample. The air sample containing the isocyanate is collected by passing air through an impinger or bubbler containing a solution of a derivatizing agent, such as PAC, or through a filter or sorbent cartridge impregnated with a derivatizing agent. After the derivatizing agent binds with the isocyanate compound, a portion of the derivatizing agent molecule is cleaved from the derivatizing agent-isocyanate derivative and the cleaved portion is detected. The cleavage reaction is performed in a manner similar to the amine deprotection reactions described in Kornblum, et al. (J. Org. Chem., 42(2): 399-400, 1977), which is incorporated by reference herein.
This method provides a distinct advantage over the isocyanate detection methods currently used by those skilled in the art because all of the isocyanate derivatives yield the same molecular cleavage residue, and total isocyanate levels are measured by simply measuring the amount of cleavage residue produced. Alternatively, if measurement of individual isocyanate species is desired, the individual species can be measured after derivatization but prior to cleavage.
This method also provides an advantage over the prior art by allowing for the detection of isocyanate groups chemically bound to solid or particle surfaces, such as wood composites or polyurethane.
Accordingly, it is an object of the present invention to provide an isocyanate derivatizing agent that is capable of derivatizing all isocyanate species.
It is another object of the present invention to provide an efficient method for producing the isocyanate derivatizing agent 9-anthracenylmethyl-1-piperazinecarboxylate.
It is yet another object of the present invention to provide a rapid, sensitive, inexpensive and efficient method for the detection and quantification of isocyanates in a sample.
It is a further object of the present invention to provide an effective method for the detection of isocyanates bound to solid or particle surfaces.